Isomerization of naphthenes



I catalytic activity declines.

true but the same molecular weight.

Patented Dee. 26, 1944 UNITED J sTA'ras "P TEN OFFICE I Q IsoMamzs ri l z'tsam s I N William J. Mattox. Riverside, 111., assignor to Unlversal Oil Products Company, Chi

, corporation of Delaware can, 111., a

No Drawing. Application December 17, 1943,

' Serial No. 514,661

I 11 Claims. (01. zoo-cosy solid catalyst which possesses man advantages over the catalysts previously employed in the,

isomerization art.

hexanes in the presence of aluminum chloride and hydrogen chloride has been previously reported. For example, Schuit, Hoog, and Verhaus, J. Rec. trav. chim., 59, 793-810 (1940) report the isomerization of 1.1-dimethylcyclohexane to a mixture of 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane, and 1,4-dimethylcyclohe'xam using aluminum chloride and hydrogen chloplexes which result in high catalyst consumption.

I have now found that alkyl cyclohexanes can he successfully isomerized to alkyl cyclohexanes of diiferent molecular structure in the-presence of silica-alumina catalysts including the clay catalysts such as the naturally occurring earths,

clays, or hydrosilicates-aswell as synthetic com- DOsites of silica and alumina The silica-alumina catalysts are inexpe s ve and are easily prepared. They are easily handled in a variety-of techniques; they possess a relativelylong life: and they can be readily regenerated .when the Broadly, the invention relates to the ison'ierlzation .of alkyl cyclohexane hydrocarbons in the presence ofasilica-alumina catalyst.

. In one specific embodiment the invention comprises contacting an alkyl cyclohexane with a calcined composite of the hydrogels of silica and alumina under isomerizing conditions ofteinperature, pressure, and reaction time and recovering from the reaction products at least. one alkyl ,cyclohexane having a diiferent molecular 'struc-- 45 available. In generaL-isomerization or type 1 isobtained more readily with methyl and ethyl As will be described hereinafter in greater detail, one of the most important embodiments of mixtures thereof. ortho diethylcy'clohexane is a valuable intermediate in organic syntheses and -m a'y be converted tonaphthalene, phthalic ans hydride, orother valuable compounds.

the isomerization products will.

In general two types or isomerization of alkyl cyclohexanes is found:

(1) Shifting of intact alkyl side chains alon the cyclohexane ring as fllustrated by the follow- I 6 ins equations wh The isomerization' of certain dimethylcyclo-. emu meta and para'dlethyl' hexane.

cyclohexane are isomerized to ortho-diethylcyclo- (2) Rupture of an alkyl side chain and redistrihution of smaller alkyl radicals along the cyclohexane ring as illustrated by the'following equation wherein propylcyclohexaneis isomerized to 1,3,S-trimethylcyclohexane.

Both of the above types of isomerization are included within the scope of the present invention and both are obtained under suitably con-' trolled conditions of operation. The nature of of course, de- -pend on the charging stock, the operating conditions, and other factors. In most cases it will 40 be desirable to conduct a few small scale experiments in order to select the optimum conditions of temperature, pressure, and reaction time which are necessary to obtain the desired isomerization product from the particular charging stock which -cyciohexanes. With alkyl cyclohexanes having longer side chains there is a greater tendency to obtain the isomerizationdesignated asi-type 2.

Thus, it is within the scope oi my invention to eife'ct .the isomerization of dimethylcyclohexane tov diflerent' dimethylcyclohexanes, ethylcyclohexane to dimethylcyclohexane, diethylcyclohex ane to diflerent diethylcyclohexanes,diethylcycloso hexane to tetramethylcyclohexane, normal-pro- -The effluent reaction pylcyclohexane to trlmethylcyclohexane, isopropylcyclohexane to trimethylcyclohexane, propylcyclohexa-ne to methylethylcyclohexane, normal, secondary, or tertiary butyl cyclohexane to tetramethylcyclohexanes, amylcyclohexane to pentamethylcyclohexane, etc.

The catalysts employed in the present process comprise broadly silica-alumina composites or, as commonly referred, to, associations of silicon oxide and aluminum oxide. The naturally occurring earths and clays such as diatomaceous or infusorial earth, pumice, fullers earth, kaolin, montmorillonite, bentonite, etc., may be employed. These earths andclays are often subjci-ted is an acid pretreatment in order to increase their cataiytic activity. The preferred catalysts of t process are the synthetic composites of silica and 5a comprising generally a calcined composite of Eiydrogels of silica and alumina. These hydrogels may be prepared according to any of the methods wellknown in the art.

It is also within the scope of the invention to employ ca alysts comprising composites of silica i with other oxides, e. g. silica-alumina-zirconia,

to the process are generally found in straight run hydrocarbon fractions such as straight run gasolines. Charging stocks comprising the higher molecular weight alkyl cyclohexanes may be obtained from various hydrocarbon conversion processes, for example by the hydrogenation of alkyl benzenes obtained from various benzene alkylation steps.

The isomerization of alkylcyclohexanes in the and reaction time which must be employed with the particular cl'iarging stock are Ziable. The silica-alurnina catalysts may be employed according to many of the usual hydrocarbon conversion techniques employing a solid catalyst. Under most operating conditions contamination of the silica-alumina catalyst with carbonaceous deposits is negligible. Accordingly, a convenient operating techniq ue comprises the fixed bed method of operation wherein the charging stock is passed undersuitable conditions of temperature, pressure, and flow rate through a reaction zone containing a mass of silica-alumina catalyst. products are separated by fractionatiop other suitable means; the de-- sired isomers-atlas {JiiuHjPi-S' recovered: and unconverted reactants are recycled to the reaction zone. Under relatively severe operating con ditions a certain amount or dealkylation or splitting off of alkyl side chains may occur resulting in olefin production and possible contamination of the catalyst with a carbonaceous deposit. Under such circumstances the catalyst may be readily regenerated with an oxygen-containing gas whereby to remove the carbonaceous contaminants by combustion thereof. The silicaalumina catalyst may also be employed in subdivided or powdered form according to the socalled fluidized or moving bed techniques now well-known in the hydrocarbon conversion art.

One of the most important applications of my process is in the production of ortho -diethylcyclohexane from metaor para-diethylcyclohexane or mixtures thereof. Ortho-diethylcyclohexane may be converted into naphthalene by dehydrogenation at high temperatures in the presence of catalysts comprising the oxides of the metals from groups V and VI of the periodic table, whereas metaand para-diethylcyclohexanes obviously cannot yield napthalene upon dehydrogenation. If ortho-diethylcyclohexane is dehydrogenated at relatively low temperatures in the presence of nickel, platinum, or palladium catalysts the corresponding alkyl aromatic hydrocarbon is formed which upon oxidation may be converted to phthalic anhydride.

The following example is given to illustrate the latter embodiment of my invention but it is in no way intended to limit the generally broad scope of the invention.

A diethylcyclohexane fraction consisting essentially of the meta and para isomers was vaporized and passed at atmospheric pressure over a synthetic silica-alumina composite obtained by calcining a mixture of the hydrogels of silica and alumina. The temperature in the reaction zone was 400 C. and the liquid hourly space velocity defined as the volumes of liquid hydrocarbon passed through the catalyst zone per volume of catalyst per hour was approximately 0.5.

The total reaction products after 2 hours of operation were subjected to fractional distillation, and 63% by volume of a diethylcyclohexane fraction was separated which contained approximately 50% ortho-diethylcyclohexane. Two representative cuts from the diethylcyclohexane fraction in the product had refractive indices at 20 C. of 1.4460 and 1.4438. Further proof of the presence of the ortho-diethyl-cyclohexane was obtained by dehydrogenation to naphthalene in the presence of a chromia-alumina catalyst.

I claim as my invention:

1. An isomerization process which comprises contacting an alkylcyclohexane with a silicaalumina catalyst under isomerizing conditions I" and recovering from the reaction products at least one alkylcyclohexane having a different molecular structure and the same molecular weight as the alkylcyclohexane originally charged.

2. The process of claim 1 wherein the isomerization products comprise at least one alkylcyclohexane wherein the alkyl side chains contain the same number of carbon atoms as the alkylcyclohexane originally charged.

3. The process of claim 1 wherein the isomerization products comprise at least one alkylcyclohexane containing an alkylside chain of fewer carbon atoms than a side chain of the alkylcyclohexane originally charged.

4. The process of claim 1 wherein said isomerization is conducted at a temperature of from about 250 C. to about 550 C.

5. The process of claim 1 wherein the catalyst of silica and alumina.

contacting para-diethylcyclohexan'e with a silica- 6. The process or claim 1 wherein the catalyst comprises a clay catalyst.

'7. The process of claim 1 wherein the alkylcyclohexane charged comprises-a methylcycloalumina catalyst under isomerizing conditions and recovering ortho-diethylcyclohexane from I the reaction products.

11. An isomerization process which comprises contacting an alkylcyclohexane with a silicacontaining catalystunder isomerizing conditions and recovering from the reaction products at least one alkylcyclohexane having a different molecular structure and the same molecular weight as the allwlcyciohexane originally charged.

WILLIAM J. m'rrox. 

